Craft locating apparatus



NOV. 22, 1949 J, HERBOLD 2,489,221

CRAFT LOCA T I NG APPARATUS Filed June 26, 1945 4 Sheets-Sheet l F. 01 8 "D9" or g Rob 91% I. Her bo ld.

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(Ittomeg N 1949 R. J. HERBOLD 2,489,221

CRAFT LOCATING APPARATUS Filed June 26, 1945 4 Sheets-Sheet 2 lhwentor ROBE RT J. HERBOLD (Ittomeg 1949 R. J. HERBOLD CRAFT LOCATING APPARATUS 4 Sheets-Sheet 25 Filed June 26, 1945 1 29-2119. Robefl lHerbold QQM R M (Ittomeg Nov. 22, 1949 R J, HERBQ D 2,489,221

CRAFT LOCATING APPARATUS Filed June 26, 1945 4 Sheets-Sheet 4 Fz ri 6.

Zhmentor Robel t J. Herbold Gttomeg Patented Nov. 22, 1949..

UNlTED STATES PAT ENT OFFICE 2,489,221 1 0mm: LOCATING Arrsm'ms Robert J. Her-bold, Denver, 0016... asslgnor to Lafayette M. Hughes, Denver, Colo.

7 Application June 26, 1945, Serial No. 601,686

9 Claims. (01. 33-46) This invention relates to mechanism for the guidance'of craft, and more particularly to a device which will aid the pilot in holding his craft in proper formation in spite of clouds, fog and adverse weather conditions which prevent him from seeing the accompanying craft.

When aircraft are flying together in large numbers, it is essential that they maintain a geometrical formation for their guidance and to prevent collisions, or if they are in combat, to maintain a certain protective association with one another. However, when passing through extensive and dense clouds, the pilots cannot see the beacons on other craft,and while flying blind may get out of formation with serious results; and it is sometimes found that a pilot may be so confused by the darkness of the'heavy clouds, whether during the day or night, that he loses his sense of direction and may get-entirely away from the formation and become lost. For many reasons, it is often imperative that the pilot maintain either a visual or an instrument contact.

with the adjacent or associated aircraft during flight. The same considerations apply to boats at sea which are required to travel in a convoy or through a tortuous channel entrance to a harbor or otherwise to maintain a desired position relative to other boats or objects carrying beacon or guiding lights.

The primary object of this invention is to provide apparatus which informs the pilot of a craft as to the location of a guiding beacon and thereby aid him in maintaining a proper course.

A further object of the invention is to provide a craft with a guidance instrument which figuratively sees identifying beacon signals on accompanying craft and gives the pilot an indication as to the directive location of the other craft.

A further object of the invention is to provide a guidance instrument which determines the directive positions of guiding beacons on associated craft and triangulates their angular directions into an indication of the approximate distance thereof.

Another object of the invention is to provide aircraft with guidance instruments which will give the pilot an indication of the positions of aircraft which are flying at the same elevation or in planes above or below him, and which will guide him in maintaining a proper flight formation while he is flying blind through dense clouds or at night. Further objects will be apparent in the following disclosure.

In accordance with my invention, I propose to a craft which pick up and indicate the direction of a guiding light beacon, and by triangulation of the angles of the two directive lines to the beacon show approximately the position and the distance thereof. In the application of this principle to the guidance ofaircraft in flight formation or of boats in a convoy, I provide a light beacon on each craft which is so located as to be seen'from an adjacent craft; and each craft is provided with several photo sensitive elements and associated electrical apparatus which are so constructed and arranged that indicating devices governed by the photo elements give the required location of the beacon on another craft. These indications are determined by a variation in electrical characteristics of the circuit which change with a change in the angularity of direction of the light ray that strikes the receiving photosensitive element. For this purpose, I prefer to employ the type of apparatus shown in my co-pending application, Serial Number 582,918 filed March 15, 1945, but I may utilize the constructions shown in my other co-pending applications #562,353, filed November 7, 1944, and #570,169, filed December 28, 1944, and which are modified as herein described in order to give the desired indication or guidance control of the pilot or the craft.

Referring to the drawings which illustrate a preferred embodiment of this invention as applied to the guidance of aircraft in flight formaion:

Fig. 1 is a diagrammatic plan view of three aircraft carrying the beacons and photosensitive pick-up elements and illustrating the principles involved in holding the craft in flight formation;

Fig. 2 is a. vertical rear elevation of two of the craft of Fig. 1;

Fig. 3 is a vertical elevation of a standard photosensitive tube;

Fig. 4 is a transverse section on the line 4-4 of Fig. 3;

Fig. 5 is a vertical elevation of a new type of photo tube having a triangularly shapedcathode;

Fig. 6 is a section on the line 66 of Fig. 5;

Fig. 7 is a vertical elevation of a modified form of my tube;

Fig. 8 is a section on the line 8-8 of Fig. '7;

Fig. 9 is a diagrammatic view showing how a light in two positions A and B may activate different but equal areas of the cathode of a standard phototube of Fig. 3, the right hand portion of the figure showing the cathode turned at right angles to illustrate the area of activation;

employ two spaced photo sensitive elements on It Fig. 10 is a similar diagrammatic view showing 3 v be relationship of the two positions of the light the activated areas of the trianmfl r cathode f F18. "I; a

Fig. 11 is a similar view showing the activated reas on the cathode of Fig.

Fig. 12 is a wiring diagram of a preferred type f electric circuit for determining the direction f another craft;

Fig. 13 is a schematic wiring diagram of the arious phototube circuits on the aircraft;

Fig. 14 is a diagrammatic fragmentary plan iew, partly in section, of one wing showing the eacon light and the two setsof receiving photoubes;

Fig. 15 is a fragmentary vertical section of the ring and itsbeacon light; a

Fig. 16 is a. fragmentary side elevation, partly section, of the rudder section of the plane;

Fig. 1"! is a fragmentary vertical section of the udder section; and

Fig. 18 is a diagrammatic view of a photoube amplifier circuit having a special photo tube onstruction.

The main principles of a specific embodiment I this invention are illustrated in Figs. 1 and 2 rhich show diagrammatically the relationship f three aircraft in flight formation. These raft, designated by the numerals I, II and III, re each provided with two beacon lights I and located ad,acent to the tips of its wings and a a line at right angles to the direction of flight. .he lights, which may be'electric bulbs of 50 or more candle power, such as are used for automobile headlights, and which preferably give a iigh emission of infrared rays, are so mounted see Figs-l4 and 15) that they may be observed rom opposite sides of the aircraft only within a 40 spherical angle directed outwardly; and the eacons are unobstructed so that each may be een from above and below as well as laterally within that angle. The beacon lights are obcured within the remaining spherical angle of .20, so that only one light will be picked up \ormally by the observing craft on either side hereof. Two pairs of photosensitive elements 3 .nd associated electrical apparatus are so ated and shielded in each quadrant on each of he aircraft that they will simultaneously pick 1p one of the two beacon lights on the wings of be next adjacent craft and through suitable :lectrical instruments indicate the angular diection of the light. The electrical apparatus .lso triangulates automatically the two observed lirections of the beacon light into an indication f its position or distance and the location or iltitude above or below the observing craft. A bird pair of photo elements (Fig. 2) in each uadrant gives the relative elevation.

The eight pairs of photo-sensitive elements 3, leslgnated in Fig. 1 by small triangles; are prefirably mounted on each side of the nose and in he tail of the aircraft and at the front and the 'ear of each wing tip; and these are shielded by lcreens having slots 4 therein which give an )ptical vision, as it'were, of all possible locations if the beacons. Each photo element (see Fig. 14) 18.5 a spherical angle of vision of 125", more or ass as desired, so that the two pairs of photo :lements facing into agiven quadrant can pick 1p a beacon within that quadrant. The angle cetween the lines a and b, taken with the distance between the photo elements d and e on :raft II, will serve for calculating the distance, as well as' indicating the direction, of light 2 on craft 1. Similarly, craft 1 can determine the dis- 4 R tance and location of beacon l of craft-II by means of the rear photo elements in the right vwing and the right hand elements in the tail. Thus each craft has an instrument vision of' a beacon on the craft on each side of it. These orother photo sensitive elementsmay be mounted on the craft in any desired locations to insure having no blind spots.

In order thatthe directive angularity of the beacons may be determined automatically, I may use photosensitive elements of the photoemissive,

photoconductive or photovoltaic type, which are so constructed and arranged that an electrical characteristic is varied with the direction of a light ray impinging thereon. The construction herein described is a photoemissive element so shaped and arranged relative to the slot 1 in its shield that the electron emission and the resultmade of glass or other material provided with a base It and the supportin prongs it. One prong may be electrically connected with the cathode, and the anode may be connected with a cap H3 at the top of the tube. The photosensitive inner surface of the cathode may have a coating of a suitable metal, comprising lithium, sodium, potassium, rubidium or caesium, the choice of which depends largely upon the type of light to be received. For light from a standard electric light bulb, and particularly one which gives a high emission of infra red rays, aslis' pf!- ferred, the cathode may be made of a base metal of silver coated with caesium on caesium oxide.

If that standard tube of Figs. 3 and 4 is connected in a suitable circuit, as will be explained, and if the cathode receives light rays through an elongated aperture 4 (Fig. 9) in a wall l8, then whenthe light source I9 is moved from position A to position B, the light rays will fall upon equal areas C and D of the cathode 9, disregarding the angles of incidence of the rays, and the electron emission will be the same for either angular position of the light. If, however, the cathode is made substantially triangular in shape and bent'in an arc and arranged as shown in Figs.

11 will illuminate a large area E at the wide end of the cathode l 0 and only a small area F when in position B. Similarly, Fig. 10 shows how the triangular cathode ill of Figs. 7 and 8 will be illuminated. Hence, the electron emission and the resultant current will vary progressively as the apparent light position is moved.- I employ this principle to determine the position and the relative distance of the beacon light being observed.

A photoemissive tube of this new type may be made as shown in Figs. 5 and 6, in which the cathode I0 is substantially triangular in shape, but preferably bent in a concave cylindrical arc, with its greatest width at the left hand side and tapering to a narrow width at the right hand side. The cathode may be rectangular or otherwise shaped and only a tapered area: thereof may be coated with the light sensitive material; or

opaque material may be applied to a standard to obstruct materially the passage of the light rays or to cast a wide shadow on the cathode."

In this construction, the cathode I is suitably suspended from the top and connected to a cap 23 on the outsideof the tube casing 24. The anode loop may be supported on a vertical wire connected to one of the prongs 25 which serve to mount the unit on the base, or the connections and supports may be reversed. The tube casin 24 may be a standard light transmittlngenvelope of glass, or if it is made of opaque material, it may comprise a light transmitting window.

The cathode l0 may be shaped and arranged as shown in Figs. 7 and 8 with its wider base portion at the bottom and its narrower portion at the top and bent in a concave arc with its axis parallel or coinciding with the axis of the substantially cylindrical tube casing 24. The

anode 21 may be either a straight wire or a loop. The phototube of Fig. operates with the axis of the tube casing 24 parallel with the long dimension of the aperture slot 4 in the wall, i8 (Fig. 11) while the tube of Fig. 7 is arranged with the axis of the tube casing 24 perpendicular to the aperture slot (Fig. so that the light beam may in each case travel from the wide to the narrow end of the triangular shape. The cathode in this special type of tube may be made similar to the cathode of a standard tube as above described, such as a silver plate coated with caesium on caesium oxide. I prefer that the photo tube carrying this trianeularly shaped cathode be made the same as the standard phototube employed in my electric circuits, so that the differences in action between the two tubes will be governed solely by the area of the activated portion of each cathode.

This special type of photoemissive tube is employed to govern desired indicating or control apparatus that guides the aircraft or its pilot. This is preferably accomplished by applying a required voltage to the photoemissive tube so that when activated it will permit a current to flow. If a photovoltaic cell is used, it will generate current directly. Also, a photoconductive cell will require an applied current, and the current flow will depend on the resistance of the selenium or other element employed which varies with the amount of light striking its surface. This electrical signal is preferably amplified to insure satisfactory results under all atmospheric conditions, and this may be done by so arranging the phototube circuit that it controls the grid potential of an amplifier tube in a secondary power circuit which in turn operates or governs the guidance indicators or control apparatus.

In order that variations in light density caused by fog, snow, rain, dust and other atmospheric conditions may not afiect materially the operation of the device, I prefer a construction in which my special type of phototube (Figs. 5 to 8) having a triangular cathode I0 is balanced against a standard tube having a rectangular cathode 9 (Fig. 3) and the parts are so arranged in electrical circuit that any variation in angular incidence of the light beam on the two balanced tubes gives a current variation that is related to that angle. Also, by employing two balanced phototubes, the variation in current which is proportional to the cosine of the angle of incidence of the light affects these two cathods alike, and'thus that factor of a variable angle of illumination is cancelled or minimized.

In its electric circuits, the device is comparatively simple. Referring first to Fig. 12, which shows the circuits for one of the distance and direction indicating needles in quadrants A, B, C and D of the circular dial of Fig. 13,-! have balanced a standard vacuum phototube 24 having a rectangular cathode i (Fig. 3) against my special type of vacuum phototube 3| having a triangular cathode l0 (Figs. 5 and 7) by connecting the two tubes in series with a source of power in a bridge circuit so that one acts as the load for the other. Each of the tubes is so arranged on the aircraft that their cathodes point at the same angle toward the beacon light. A battery 32, or other suitable source of power, has its negative terminal connected to the specially shaped cathode Ill and its positive terminal con- A nected to the anode l2 of the standard tube. potentiometer resistance 33 connects across the terminals of the battery, and an adjustable contact 34 for the resistance is grounded into the framework of the aircraft. The vacuum phototubes are operated at saturation voltage and the maximum cathode emission for the weakest light condition and the current voltage characteristics are such that the circuit is very sensitive and the difierence in light reception of the two cathodes gives a large change in voltage. That is, the cathode gives a saturation current under all normal conditions of use, and any variation in light intensity as caused by fog, rain or snow will not affect the indicator reading.

In this arrangement, if one tube receives more light than the other, its resistance decreases and the voltage distribution between the two tubes changes. That voltage variation in the phototube circuit is employed to vary the potential of a grid 35 of a suitable amplifying tube 36, such as the standard pentode illustrated diagrammatically in the drawings. The cathode 38 of the pentode is grounded to the framework as shown, and it is indirectly heated by a filament wire 39 to which A. C. or D. C. current is suitably applied.

In this construction, a screen grid 40, connected to the cathode, and a suppressor grid 4| are 10- cated between the main grid 35 and the anode plate 42, and the parts are suitably mounted and arranged as is well understood. A battery 45 of suitable voltage is grounded at its negative terminal and connected as illustrated to supply the necessary current and potentials to the electrodes and grids of the amplifying tube 36. The parts are so constructed and arranged that when the potential of the grid 35, which is normally biased to a negative condition, is made less negative by the phototube circuit, the electron emission from the heated cathode 38 will be increased greatly and pass to the anode plate 42, and current derived from the battery 45 will flow-and actuate the needle 48 of a milliammeter 49 of suitable construction, such as a galvanometer. The contact arm 34 of the potentiometer resistance may be adjusted to give the proper readings for, a standard flight formation. For example, the potentiometer contact 34, as well as the amplifier circuit, is balanced to give a middle reading for the ammeter needle when the v-shaped cathode Ill of the special phototube receives light at about its middle portion G (Fig. 10) and thus gives an electron emission intermediate between the values obtained when the light beam activates the opposite ends of the cathode.

For indicating the altitude or relative vertical position of the observed craft, I may employ a similar circuit arrangement comprising two sets ioto tubes located forward-and the other to the rear." The wires 'om the forward set are connectedin multiple the wires II from the other set, as indid in Fig. 13 so that onlyone needle 82 is led to indicate the relative altitude of a plane er in front or behind the observing plane on one side thereof. These needles 52 are My arranged on an instrument 53 of the :sonval' type of galvanometer. The needle be bent at right angles near its outer ,end so I as it revolves about its pivot the needle els parallel with itself over the indicator dial. i type of galvanometer is shown at I. in Fig.

desired, I may utilize flashing or chopped ts for the beacons I and 2 which flash at a wn frequency, such as 600 cycles per minute, in that case the electronic apparatus is tuned to that frequency so as to eliminate the :ts of stray light. The chopped or interently flashing light may be produced by plac- In front of the light bulbs I and 2 a rotating. provided with light apertures, which is rod by a constant speed electric motor. Also, intermittent flashes can be obtained from a cury arc type of light. To tune the receiving uit thereto, I may make use of a band pass r of suitable construction. This may be d in the photo tube grid circuit and arranged ass only a pulsating direct current. Such a r, as shown in Fig. 12, may be located in the leading to the grid ll. A standard type of r comprises an inductance coil ii in series a condenser 58 in parallel which form a low filter, and a condenser 51 in series and an ictance coil 58 in parallel which form a high l filter. The resonant circuit comprising the 58 and condenser 58 is grounded at 69 and :iected by a wire 60 to the line leading from coil 55 and condenser 51 to-the grid 35. The it offers but littie impedame to a low fre= :icy pulsating direct current and a high imance to ahigh frequency current. The caity 5! in parallel prevents the low frequency -ent from being shunted across the line. Simly, the condenser 61 stops a non-pulsating ct current, but it does not impede a high ,uency pulsating direct current; and the latter ts a high impedance in the shunt inductance Suitable selections or adjustments of the intances and capacities will tune the circuit ieeded. When the flashing light is used, the ium phototube is activated intermittently and :ives an instantaneous electron emission in :hronism with the chopped light, which res in a pulsating variation of the potential of amplifier grid 35. The indicating instruments and 53 are of suitable construction, such as DArsonval galvanometer, for measuring the iating direct current. If desired, a vacuum de amplifier may be inserted ahead of the tode to give a two stage amplification, and ind pass fllter may be used with each amplifier. my elaborations or modifications of this conlction will be apparent to one skilled in eleciics.

.eferring now to Figs. 13 to 1'7 inclusive, I e there shown diagrammatically the arrangeit of these various phototube circuits and the trolled instruments. One composite instruit seen by the aircraft pilot may comprise an guidance needles (Fig. 13) arranged to give approximate directional location of adjacent raft in any one of the four quadrants of ineach wing, one set pointthe pilot's horizon. That is, the circular panel I boardmay be divided into the quadrants A, B, C and D. The operationand' construction in each of these quadrants is the same. in the right handrear quadrant C 'on aircraft II of Fig. 1, the light I of plane III is viewed by the rear right phototube I in the tail of craft II andby the rearphototube in the right wing of the same craft. The electrical apparatus is so constructed and arranged that one needle 84 of quadrant C (Fig. 13) points in an angular direction related to that of the line e between craft II and III of. Fig. 1 and the other needle I,

takesa direction related to the direction I of Fig. 1. Thus, the point where the needles, and II cross may be considered as giving the location of the beacon I, and the panel board may be so calibrated as to indicate the approximate distance of that beacon from the observing aircraft. Similarly, in the upper left hand quadrant A of aircraft II, the needle 66 gives the direction of the light 2 of craft I from the nose of plane II and the needle '81 gives the direction of the same light from the left hand wing phototube. Thus, the pilot of craft II can observe his position relative to the two crafts I and III in the formation and can guide his craft accordingly.

A single needle 66 (Fig. 13) may be pivoted centrally between quadrants A and B and arranged to swing into either quadrant. Hence, only seven instruments are shown. Each of the needles is governed by a separate phototube circult of the type shown in Fig. 12. The double lines of Fig. 13 which lead from the instrument panel to the different parts of the plane indicate the arrangement and need not be further described. The panel 53 carries a zero mark shown as a silhouette of an airplane, and the positions of two needles 52 relative thereto indicates the altitude or relative position of an accompanying plane as to whether it is in the same or above or beiow the piano of the observing craft.

The constructional details may be as desired. As shown in Figs. 14 to 17, each of the light bulbs I and 2 may be suitably mounted and shielded in the tip ends of the wings. The electric light bulb may be protected by a suitable transparent wall it conforming properly with the outline of the wing, and shielding and supporting walls 'II are arranged to confine the light rays to the spherical angle of about 240 to 280, as shown in Figs. 14 and 15. Electric current is suitably transmitted from a battery or an A. C. or D. C. dynamo.

In each of the wing tips (Figs. 14 and 15) and out of the path of the lights I and 2,,I mount four pairs of the associated phototubes of Fig. 12, two pairs facing forward and the other two pairs pointing rearwardly. The two front phototubes 12, one behind'the other, control the circuit for quadrant B needle I3 (Fig. 13) and the other two tubes 14 govern the altimeter needle 52. The slot 4 for tubes 12' is vertical and the walls are so spaced that these tubes pick up light rays within an angle of about 125 from a. line running at right angles to the direction of travel. Thus these two tubes and the corresponding tubes in the other wing see all that is in front of the aircraft. It will also be noted that the tube sets 12 at the rear of the wing are arranged to pick up light rays which are 15 or 20 degrees outside of the quadrant as indicated by the dotted lines and angle measurements, so that this overlapping prevents another plane from getting into a blind spot. The slot 4 for the other pair of tubes 14 For example, i

is horizontal and arranged so that these tubes pick up aircraft above and below the observing craft within a suitable angle such as about 125. These tubes and the corresponding ones pointing rearwardly (Fig. 14) are arranged to warn of danger of collision from craft flying at different levels. These tubes connect with circuits 50 and and control needle 52. The two sets of tubes are suitably mounted within a receptacle 15, which may be gyroscopically supported so that it is not affected by lateraltilting of the plane or pitching thereof, andthe gyroscopes and associated parts may be suitably constructed. The phototube amplifier apparatus is indicated by the rectangle l6. n

This same general construction is to be found at each side in the tail of the aircraft, as shown in Figs. 16 and 17 and the tubes and circuits in the nose may be similarly arranged. The phototubes having cathodes 18 and 19 and an associated amplifier tube 36 are suitably mounted on a panel board 80 and behind the narrow vertical slot ll arranged to give a view of about 125 from the direction of flight, so that the two sets on the opposite sides of a partition 82 view all behind a center line perpendicular to the direction of travel. As shown in Fig. 13, the tail tubes govern the needle 64 in quadrant C and the corresponding needle in quadrant D. The other needle is governed from the rear wing tubes.

A modification of the photo tube construction is shown in Fig. 18. That is. I may employ two photo tubes having their'triangular or tapering cathodes 85 and 86 of the same shape and size but arranged with the tapers extending in reverse directions so that light passing through the slot 4 will activate equal areas of the two cathodes only when it reaches the central portions thereof.

The rest of the construction may be made as above described, and either with or without a band pass filter. A DArsonval galvanometer 88 of standard construction is shown diagrammatically. Oblique light rays have a multiplied effect because of the reverse taper, since movement of the light ray up the two cathodes gives a reduced activation for one cathode and an increased activation for the other. This arrangement diminishes the effect of stray or ambient light, because the areas of the cathodes are equal and any variation in ambient light balances out. Various other arrangements may be employed, such as using the standard rectangular cathodes in association with two sets of opaque screens, one of which has a slot 4 as above described and the other of which has a tapered opening, similar to the tapered cathodes above described, so that as the light travels through the slot and thence through the tapered opening it activates a larger or smaller area, depending upon the angle of direction.

It may also be observed that the more distant or stray lights do not materially affect the readings of the instruments, since the predominating or closest light to the photo tube will largely control the cathode activation. That is, if one light is 50 feet from a pick up unit and another is 100 feet away, the latter will not aifect the meter reading sufiiciently to hamper the guidance of the aircraft, and particularly since it is not necessary to make accurate observations of distance or direction but merely to indicate zones of safe and unsafe operation and to provide warning signals which tell the pilot the approximate location of the accompanying craft.

In place of the photoemissive tubes above described, I may use a photoconductive cell comprising a selenium resistance which causes variation in a current derived from a battery. I'may also use a photovoltaic element, such as a copper oxide cell or a Weston photronic cell for the electron emission. The photovoltaic cell has the advantage of not requiring any source of electric power. Thelight activated surface of the photovoltaic cell may have a triangular shape as above described. Similarly, that portion of the selenium cell which is to be activated by light may have an opaque screen providing the triangular shape, so that as the light angle changes the cell resistance will likewise change.

The size of the slot! depends on the sizes of the associated cathodes and their locations, but for a standard size of photo tube arranged close to the slot, I prefer that the width of the-slot be about one-eighth of the height of the cathode so as to provide enough electron emission for more than a safe flying distance from the accompanying aircraft. A standard Mazda 50 candle power lamp gives enough infra red light to penetrate a dense cloud or rain or snowstorm and activate the phototubes at 1,000 feet or a far greater distance than needed for a flying formation. Also, various optical devices, such as collector lenses, may be employed to direct or to concentrate the light and to supplement the amplifier tube.

For the phototube. I may use a standard vacuum tube or a tube filled with ar on or other as. The amplifier tube is preferably of thovacuum type. Also, instead of batteries or a D. C. generator for the phototube amplifier circuit, I may use a source of alternating current. with a condenser connected between the phototubes and amplifier cathode, with one plate connected to the grid 35. Many changes in the circuit and the types of apparatus used will be readily apparent. I may use the apparatus of any of my above-mentioned prior applications for the present purposes, and thereby obtain an indication of the d rection of the beacon light and its location and distance. Another suitable construction involves the use of a cathode tube activated by a phototube ampli-. fier circuit, in which the direction or location of the beacon is shown as a light spot on a sensitive screen. In that case, the cathode tube can be swung to the required position of angularity just as the instrument needle is moved. It will also be understood that the apparatus above described may be simplified or made more complex, depending on its intended use.

In each of the constructions described, as well as those of said prior applications which are here usable when modified as herein set forth, I provide a guiding beacon. and preferably two, so located on one craft that the rays from one beacon may activate spaced photosensitive elements on another observing craft; and the photosensitive elements are so shielded that the right ones will pick up at one time only one beacon. The photosensitive elements, either directly or through an amplifier, provide current for an electric circuit connected with electrical apparatus, such as the indicators or milliammeters above described. A characteristic of that circuit, such as its amperage, is varied in a definite relation to the directive angularity of a light ray from the beacon to the photo element. In the constructions of the two first filed applications above mentioned, that electrical characteristic is the instantaneous value of a current at the time when the photo element A is activated, as provided by varying a resistance 76 according to that angular position of light activation so that the current value is related to that angularity and is translated as a measurementof distance or position. In the construction illustrated in the drawings, the current value depends on the angle of incidence of the light ray on the photo element. The angle between the lines of vision of two photo elements is translated by the' calibrated instrument as the position or distance of the observed beacon.

It is to be understood that, in the description of this invention and in the claims, any variation in illumination and in the area of activated cathode surface which arises solely from the spreading of the light beam, which varies with the cosine of the angle of light incidence, is to be disregarded," since both phototubes are affected the same bythe light falling on the two cathodes at the same angle. In that case, the more oblique the angle of incidence, the less is the illumination per unit area, and a narrow band of light will cover a greater area approaching infinity as the angle of incidence changes from a line perpendicular to the surface to parallelism therewith. Hence, the claims are to be interpreted as not referring to a variation in illumination caused by a change in the angle of incidence, but as referring to an increase or a decrease in electron emission caused respectively by an increase or decrease in the area shield which directs thereon a narrow ray of light I from an observed beacon, the light activated surfaces of the two cathodes being tapered in a reverse arrangement 50. that a varying directive angularity of the beacon ray simultaneously activates a greater area on one cathode and a lesser area on the other, an amplifier tube having its grid potential governed by the voltage distribution between said tubes, and a positioning guidance device governed by the amplifier in accordance with a variation in the angularity of the beacon ray relative to the cathodes.

12 claim 2 in which guiding beacons and shields seen at a time from an observing craft.

- 4. Craft positioning apparatus comprising a uiding beacon and a shield therefor mounted on 2. Craft positioning apparatus comprising a guiding beacon on one craft which is exposed to be seen from an observing craft, electronic apparatus including a pair of photosensitive elements and shields therefor mounted on the observing craft in definitely spaced positions where each element may be simultaneously activated by said beacon only during a limited change in angularity and distance of the beacon, two electrical direction indicating devices and circuits therefor associated respectively with said elements, means whereby each element and its shield provide a progressive variation in the activation of the element and an electrical characteristic of the associated circuit is varied progressively in a definite relation to a change in the directive angularity of the beacon ray to each activated element and the device indicates the direction of the beacon therefrom, and said indicating devices cooperating to triangulate the directions of the beacon from the related elements as the distance of the beacon from the craft.

3.v Craft positioning apparatus according to activated by light from the beacon within a a moving craft where the beacon may be seen from an observing craft, electronic apparatus including two spaced pairs of photo-sensitive elements in balanced circuits mounted on the observing craft in a definite spacing in a spherical quadrant where they may be simultaneously activated by a beacon anywhere-in that quadrant,

an electrical direction indicating device and a circuit therefor associated with each pair of elements, means including a shield for each element which provides a progressive variation in the activation of one of the elements of each pair and the unbalancing of their circuit and causes an electrical-characteristic to be varied progressively in the circuit of each device in a definite relation to a change in the directive angularity of the beacon ray relative to the pair of elements and the device to indicate the direction of the beacon therefrom, the other element of each pair serving to balance out the effect of ambient light, said devices cooperating for triangulating the indicated directions of the beacon from the two spaced element positions as the distance of the beacon from the observing craft.

5. Craft positioning apparatus comprising a guiding beacon on one craft which is exposed to be seen from an observing craft, two pairs of definitely spaced photosensitive elements mounted on the observing craft, one pair of the spaced elements being arranged for simultaneously observing the beacon in a definite spherical quadrant and another pair of spaced elements being mounted for simultaneously observing the beacon only in the adjacent quadrant, shields and mounts for the elements which permit the beacon to activate the elements of each of the pairs suc-.

cessively but continuousLv as the angularity of the beacon changes through the two quadrants. a; single indicating instrument having a separate electrical direction indicating device and a circuit therefor associated respectively with each of the elements in each quadrant, said instrument having quadrants corresponding with and identifying the quadrant of each element and its associated device, means whereby each element and its associated shield provide a progressive variation in the activation of the element and an electrical characteristic of the associated circuit is varied progressively in a definite relation to a change in the directive angularity of the beacon ray to each activated element and the associated device indicates the direction of the beacon therefrom and identifies the quadrant, said indicating devices cooperating to triangulate the directions of the beacon therefrom as the distance of the beacon from the craft.

6. Craft positioning apparatus comprising .a guiding beacon exposed on a moving craft to be seen from an observing aircraft, a photosensitive element and a shield therefor mounted on the observing craft where the element may be spherical quadrant intersected by a horizontal plane, means whereby the element and shield provide a progressive variation in the activation of the element in a definite relation to a variation in the directive an ularity of the beacon light in a vertical plane, an electrical direction indicating device including a circuit, and means including 13 amplifying apparatus governed by the variable activation of said element which varies an electrical characteristic in said circuit in response to said change in directive angula'rity and causes said device to indicate the position of the beacon relative to said horizontal plane.

7. Craft positioning apparatus comprising a guiding beacon exposed on a moving craft to be seen from an observing craft, two photosensitive elements and shields therefor mounted on the observing craft in definitely spaced positions where both elements may be simultaneously activated by said beacon anywhere in a limited spherical angle at one side of the craft during a change in angularity and distance of the beacon, a third photosensitive element anda shield therefor arranged to be activated simultaneously by said beacon within the spherical angle and on both sides of a horizontal plane, separate amplifiers and circuits governed by each element, an electrical direction indicating device and a circuit therefor associated with each element and its amplifier. and means whereby each element and its shield provide a progressive variation in the element activation and an electrical characteristic in the circuit of its indicating device is progressively varied in a definite relation to a change in the directive angularity of the beacon ray to the element so that each device indicates the direction of the beacon, vices serving for triangulating the indicated directions as the distance of the beacon and serving to give the relative vertical position of the beacon carrying craft.

8. Apparatus according to claim 7 in which the photosensitive elements and associated shields are shaped to provide a variation in the area of activation of tive angularity of the light changes and the associated amplifier is governed by the varation in activation.

said indicating deeach element as the direethat a variation in 9. Photoelectric apparatus governed according to a vvariation in the directive angularity of a light ray comprising a pair of laterally spaced photocells which are provided with light sensitive elements facing in the same direction, the light activated areas of the elements being tapered in a reverse arrangement with their directions of taper spaced and parallel, a shield having a narrow slot arranged perpendicular to said directions of taper which directs a ray of light of uniform width simultaneously onto each of the elements as the light angle changes so angularity of the ray progressively activates a greater area of one element and a lesser area of the other, an amplifier tube having its grid potential governed by the differential activation of the photocells, and an electrical device governed by the cordance with the angularity of the light my relative to the two elements.

ROBERT J. HERBOLD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,149,122 Fuller Aug. 3, 1915 1,387,850 Hammond Aug. 16, 1921 1,936,400 Langmuir Nov. 21, 1933 1,954,329 Schoenberg Apr. 10, 1934 2,077,398 Clark Apr. 20, 1937 2,147,156 Geficken et a1 Feb. 14, 1939 2,188,293 Williams Jan. 23, 1940 2,206,036 Herson July 2, 1940 2,216,716 Wlthem Oct. 1, 1940 2,220,181 Steudel et al Nov. 5,1940 2,234,329 Woifi Mar. 11, 1941 2,350,820 Rettinger -1 June 1 44 2,366,939

Smith et al. Jan. 9, 1945 amplifier in ac- 

